The present invention relates to a pad conditioner used for removing clogged or foreign substances from polishing pads in the process of polishing semiconductor substrates for planarization purpose.
In polishing of wafers, especially conventional mechanical polishing methods which are required not to cause defects, such as mechanical strain, in the wafer while keeping a desired polishing speed, it is possible to keep such polishing speed by using larger abrasive grains and/or a higher polishing load. However, because of various defects caused by polishing, it has been impossible to ensure the compatibility between keeping a desired polishing speed and no defect. Thus there was proposed a polishing method of CMP (Chemical-Mechanical Planarization). This method permits the above compatibility by a combination of mechanical and chemical polishing actions. The CMP method is widely used in the finish polishing process of silicon wafers, which requires the compatibility between keeping a desired polishing speed and no defect in the wafers. With the increasing packing density of devices in recent years, it has become necessary, in a specific manufacturing stage of integrated circuits, to polish a wafer or the surface of a semiconductor substrate in which conductive and dielectric layers are formed on the surface of a wafer. Semiconductor substrates are polished to remove surface defects such as high protuberances and roughness. Usually, this process is performed during forming various devices and integrated circuits on the wafer. This polishing process requires the compatibility between keeping a desired polishing speed and no defect like as the finish polishing process on silicon wafers. In this polishing process for the integrated circuits, the above Chemical-Mechanical Planarization (CMP) is performed by introducing chemical slurry, which gives a higher polishing removal speed and no defect characteristic to the surface of a semiconductor. In general, the CMP process includes a step which involves holding a thin and flat semiconductor material under a controlled condition of pressure and temperature on a wet abrasive surface, and rotating the semiconductor material.
In one example of the CMP process, a polishing pad is used, which comprises polyurethane resin or the like, and a chemical slurry of around pH 9 to 12, the chemical slurry being a suspension consisting of an alkaline solution, e.g. caustic soda, ammonia, amine or the like, and silica particles. Polishing is performed by bringing a semiconductor substrate into relatively rotational contact with the polishing pad while supplying a flow of the chemical slurry onto the polishing pad. When conditioning the polishing pad, closed substances and foreign substances are removed by conditioning with utilization of an abrasive tool on which diamond grains are supported by an electrodeposited layer, conditioning while supplying a flow of water or the chemical slurry onto the polishing pad.
The conditioner used in the CMP process is essentially different from conventional cutting or grinding tools in the following points. In cutting tools, even if a small number of hard abrasive grains are lost therefrom due to release, the cutting capacity is not deteriorated in the case where other hard abrasive grains remain on the fresh surface of the tools after release of the abrasive grains. In contrast, regarding the CMP conditioner, since abrasive grains released therefrom damage the surface of the semiconductor substrate, the abrasive grains are not allowed to release from the conditioner even if the number thereof is small. Further, since the CMP conditioner is used at a low rotational speed in a wet process, it does not require such heat resistance and extreme wear resistance as required to the cutting tools. With regard to conventional tools which have a problem of release of abrasive grains, there is a cutting tool in which abrasive grains, each consisting of a comparatively coarse single grain (generally, an order of not less than 1 mm of diameter), are bonded to a metallic support material. However, the conventional cutting tools are essentially different from the conditioner used in the CMP process in the following points. In contrast to the conventional cutting tools which use coarse abrasive grains, each consisting of a comparatively coarse single grain, as stated above, with regard to the conditioner used in the CMP process, abrasive grains each having a comparatively small size (50 to 300 xcexcm of diameter) are bonded to a base member of the conditioner so as to form a single surface layer. Further, since the CMP conditioner is used at a low rotational speed in a wet process, it does not require such heat resistance and extreme wear resistance as required to the cutting tools.
Conventionally, polishing pads have been conditioned by means of an abrasive tool on which diamond grains are supported by an electrodeposited nickel. Electrodeposition with nickel has been widely used because it can be relatively easily applied to metallic support materials. However, bonding strength between the electrodeposited nickel and diamond grains is not sufficient and releasing and breaking down of diamond grains often occurred so as to damage polishing pads and semiconductor substrates. Thus, a conditioner free from release of diamond grains have been sought.
In the case of the CMP polishing for producing a Shallow Trench Isolation (STI) structure or for an insulating film to be positioned between layers, for example, which poses a problem of decrease in the polishing speed especially due to clogging in the polishing pad, so-called the xe2x80x9cin situ conditioningxe2x80x9d, which is carried out during polishing, is effective in comparison with a case where polishing and conditioning are separately performed. On the other hand, however, occurrence of scratches due to release of diamond grains has become more remarkable in the xe2x80x9cin situ conditioningxe2x80x9d, thus it has been desired to establish a new xe2x80x9cin situ dressingxe2x80x9d method utilizing a conditioner without release of diamond grains.
An object of the present invention is to provide a conditioner which ensures minimum scratches, a high yield and a stable polishing speed in conditioning of polishing pads.
Under such technical background, according to the present invention, there are provided a pad conditioner for polishing pads for CMP of semiconductor substrates. A method of producing the conditioner, and a chemical-mechanical planarization method of wafers by means of the conditioner, which will be described below.
A pad conditioner is used for CMP of semiconductor substrates for performing conditioning by bringing the conditioner to slide-contact with the polishing surface of the polishing pad. A joining alloy layer covering the above surface of the conditioner supporting a group of hard abrasive grains which are embedded on the conditioner. A part of each of the hard abrasive grains is exposed to the outside of the above joining alloy layer. At the interface between the each hard abrasive grain and the above joining alloy, the surface of the hard abrasive grain is covered with a layer of either metal carbide or metal nitride.
The pad conditioner of the invention can be produced by the following method.
A first method of producing the conditioner for a polishing pad for semiconductor substrates, which comprises the steps of: preparing a support member having a surface opposed to the polishing pad, a joining alloy material comprising an active metal, and a powder of hard abrasive grains; forming a layer of the joining alloy material on the above surface of the support member; putting the powder of hard abrasive grains on the surface of the joining alloy material layer so as to uniformly distribute; inserting the support member to which the joining alloy material and the powder of hard abrasive grains are applied into a vacuum heating furnace; degassing the vacuum heating furnace to vacuum; raising the furnace temperature to the range of 650xc2x0 C. to 1200xc2x0 C. and holding it for a predetermined time to cause the respective hard abrasive grains to partially enter into the joining alloy material layer in a molten state; and lowering the furnace temperature to room temperature.
A second method of producing the pad conditioner for semiconductor substrates, which comprises the steps of: preparing a support member having a surface opposed to the polishing pad, and a powder of hard abrasive grains; preparing a powder of hard abrasive grains on each of which any one of the films selected from the group consisting of an active metal film, an active metal carbide film and an active metal nitride film is formed; forming a layer of a joining alloy material on the above surface of the support member; putting the powder of hard abrasive grains on the surface of the joining alloy material layer so as to uniformly distribute; and inserting the support member to which the joining alloy material and the powder of hard abrasive grains are applied into a vacuum heating furnace; degassing the vacuum heating furnace to vacuum; raising the furnace temperature to the range of 650xc2x0 C. to 1200xc2x0 C. and holding it for a predetermined time cause the respective hard abrasive grains to partially enter into the joining alloy material layer in a molten state; and lowering the furnace temperature to room temperature.
Ag-base and Agxe2x80x94Cu-base alloys, etc., can be used as the joining alloy. The joining alloys preferably may have 650xc2x0 to 1200xc2x0 C. melting point. The joining alloy material can be used in the form of foil, powder, etc. When a joining alloy contains 0.4 to 20 wt. % of active metal, in particular, at least one selected from the group consisting of titanium, chromium and zirconium, hard abrasive grains which are not subjected to any preparatory surface treatment are frequently used as the raw material. When a joining alloy does not contain active metals, it is necessary to subject hard abrasive grains as the raw material to preparatory surface treatment. As the preparatory surface treatment it is recommendable to apply a film composed of the above active metals or a film composed of carbides or nitrides of the above active metals to the surfaces of the hard abrasive grains as the material by the ion plating method, vacuum deposition method, sputtering method, CVD method, etc. The range of film thickness is preferably from 0.1 to 10 xcexcm. Diamond grains, cubic boron nitride (BN) grains, boron carbide (B4C) grains or silicon carbide (SiC) grains are preferable as hard abrasive grains. Sizes of grains preferably range from 50 xcexcm to 300 xcexcm. The average grain intervals of the grains applied to the conditioner are preferably 0.1 to 10 times the grain size and more preferably 0.3 to 5 times the grain size.
Stainless steels of high resistance are preferable as the material for the above support member. The use of ferritic stainless steels, in particular, is favorable for handling conditioners by making use of magnetic properties.
Furthermore, according to the pad conditioner of the present invention, the releasing of hard abrasive grains hardly occur easily during conditioning. Therefore, a decrease in the wafer polishing speed due to the loading of a polishing pad can be effectively improved by performing conditioning by means of the above conditioner as a simultaneous and parallel operation during the planarization, by chemical-mechanical polishing, of the surface of a semiconductor substrate in which a semiconductor device composed of conductive and dielectric layers is formed on the surface of a wafer.